Gas turbine engines have airfoils in the compressor and turbine sections, including stationary vanes and rotating blades. Each airfoil is mounted to a platform at one or both ends of the airfoil. Each platform has an endwall that is transverse to the airfoil at its intersection with the airfoil. A gas flow over the airfoil and endwall includes a slow-moving boundary layer adjacent to the gas path surfaces. This creates shear in the flow relative to faster moving gas away from the surfaces. A horseshoe vortex having two legs is generated around the leading edge of the airfoil at the endwall. One leg of the horseshoe vortex extends from the pressure side and across the passage on the endwall surface toward the suction side of the adjacent airfoil, and another leg extends along the suction side of the airfoil. These vortices migrate, expand, and interact with adjacent vortices, creating drag and increasing cooling requirements.
Attempts have been made to eliminate or reduce these vortices. Dielectric barrier plasma generators are known to induce flow in a neutral gas via momentum transfer from an ionized gas moving from an exposed electrode to an insulated electrode. US patent publication 2008/0145210 describes plasma generators mounted in a fillet between the leading edge and the endwall. They produce plasma extending over a portion of the fillet in the leading edge region to reduce the initiation of horseshoe vortices. Other methods to reduce the vortices include contouring the endwall as described in US patent publication 2007/0258810 and U.S. Pat. No. 7,134,842. The present inventors recognized that improvement on these prior technologies is possible.